Oak Tree: Nature's Greatest Survivor

0:00:02 > 0:00:04One tree is an icon of the British countryside.

0:00:05 > 0:00:07It is, of course, the oak.

0:00:10 > 0:00:14Today, we begin an extraordinary experiment -

0:00:14 > 0:00:20we want to understand this species as never before and to do that,

0:00:20 > 0:00:25we will film this one remarkable specimen for an entire year.

0:00:28 > 0:00:32Armed with the latest technology, we will investigate how our oak

0:00:32 > 0:00:36battles to survive through four very different seasons.

0:00:36 > 0:00:39In autumn, we go underground to see how its root

0:00:39 > 0:00:42stocks up on precious resources.

0:00:42 > 0:00:45What we're looking at is a highly dynamic system.

0:00:45 > 0:00:48In winter, we discover the sophisticated strategies

0:00:48 > 0:00:52our tree uses to take on everything the elements can throw at it.

0:00:54 > 0:00:57In spring, we find out how it senses the world

0:00:57 > 0:01:01- and how it even has its own form of language.- It talks to itself.

0:01:01 > 0:01:05There's a chattering that goes on across the whole canopy.

0:01:05 > 0:01:09And in summer, we'll see it fight predators

0:01:09 > 0:01:11hellbent on eating it alive.

0:01:13 > 0:01:18Over the next 12 months, I want to see the world as our tree does

0:01:18 > 0:01:19and tell its amazing story.

0:01:19 > 0:01:21Wow!

0:01:21 > 0:01:25In the coming year, I can't predict exactly how well it will fare,

0:01:25 > 0:01:28badly or well, but I can promise you one thing -

0:01:28 > 0:01:32you will never look at an oak tree in the same way again.

0:01:55 > 0:01:58The oak we've chosen to follow for our year-long experiment

0:01:58 > 0:02:01stands in Wytham Woods, just outside Oxford.

0:02:03 > 0:02:05It's a rather special tree.

0:02:07 > 0:02:10For a start, it's almost 400 years old.

0:02:11 > 0:02:15That means it was a sapling during the battles of the English Civil War.

0:02:17 > 0:02:21It was laying down its roots as Isaac Newton described gravity.

0:02:23 > 0:02:27And it matured as Britain underwent its Industrial Revolution.

0:02:30 > 0:02:33What's more, our oak is in a rather special place.

0:02:35 > 0:02:38In 1942, the University of Oxford

0:02:38 > 0:02:41acquired Wytham Woods, our oak's home,

0:02:41 > 0:02:45specifically so scientists could research British woodland.

0:02:47 > 0:02:49And I know these woods extremely well.

0:02:49 > 0:02:52I taught biology at Oxford for 20 years

0:02:52 > 0:02:54and my students and I used to come and study

0:02:54 > 0:02:57the countless insects that live here.

0:02:59 > 0:03:02The climate, bird populations, the soil -

0:03:02 > 0:03:05scientists know a lot about Wytham

0:03:05 > 0:03:08and this will help us better understand our tree

0:03:08 > 0:03:11and how it changes as we follow it through the year.

0:03:22 > 0:03:25Our year-long experiment begins in late August

0:03:25 > 0:03:29and the first task is to assess our tree's condition.

0:03:29 > 0:03:32To do this, forestry scientists Dr Mat Disney and Dr Eric Casella

0:03:32 > 0:03:38will create an incredibly accurate three-dimensional map of our tree.

0:03:38 > 0:03:42This is done by firing almost two billion pulses

0:03:42 > 0:03:44of laser light at our oak.

0:03:47 > 0:03:53The end result is this beautiful image - a virtual oak.

0:04:00 > 0:04:04A year from now, it will help us find out how our oak has fared,

0:04:04 > 0:04:07how much it's grown and how much new wood it's made,

0:04:07 > 0:04:10even how much oxygen it's released.

0:04:15 > 0:04:17We get some information straight away.

0:04:17 > 0:04:21Our tree is some 19 metres tall and 30 metres wide.

0:04:23 > 0:04:25But for me, there's another quite astonishing

0:04:25 > 0:04:28and quite unexpected detail.

0:04:30 > 0:04:34One of the really interesting things that we can get from these data

0:04:34 > 0:04:36is we can estimate the total number of leaves on the tree

0:04:36 > 0:04:39- and then from that... - Without counting them?

0:04:39 > 0:04:41Without counting them manually and I tell you,

0:04:41 > 0:04:46I have manually counted leaves on an oak tree just recently

0:04:46 > 0:04:49and it's not a fun job and being able to do it in an automatic way

0:04:49 > 0:04:52without having to get your hands dirty is far preferable.

0:04:52 > 0:04:53Come on, tell me, how many?

0:04:53 > 0:04:58Well, we think there are around 700,000 leaves on this tree.

0:04:58 > 0:05:03To me, the fact that you can tell how many leaves this tree has got

0:05:03 > 0:05:07- is just incredible. - It's amazing, isn't it?

0:05:07 > 0:05:12The total area of those leaves is about 700 metres squared so,

0:05:12 > 0:05:13to put that in a bit of context,

0:05:13 > 0:05:17that's about three tennis courts worth of leaf area.

0:05:20 > 0:05:23Our oak needs all these leaves because they capture sunlight,

0:05:23 > 0:05:25the source of all its energy.

0:05:28 > 0:05:32But now, in late August, our tree is acutely aware that sunlight

0:05:32 > 0:05:35will soon become a precious commodity.

0:05:42 > 0:05:45As autumn approaches, the days shorten

0:05:45 > 0:05:47and the temperature begins to drop.

0:05:53 > 0:05:56To survive, our oak must transform itself.

0:06:18 > 0:06:21Well, it may look as if not much is happening,

0:06:21 > 0:06:25but all across our tree, a dramatic process is taking place.

0:06:25 > 0:06:29Our oak is beginning a colossal redistribution of its resources.

0:06:29 > 0:06:33Well, it's been through this process hundreds of times before,

0:06:33 > 0:06:35but each time is no less challenging.

0:06:40 > 0:06:42To see what our oak is really up to,

0:06:42 > 0:06:45we need to see what is going on beneath its bark.

0:06:48 > 0:06:50BUZZING

0:06:52 > 0:06:55As autumn begins, throughout all of the branches and leaves,

0:06:55 > 0:06:59a hubbub of chemical messages are now being sent and received.

0:07:03 > 0:07:06These chemicals are known as hormones and our tree is producing them

0:07:06 > 0:07:08to prepare itself for the autumn.

0:07:13 > 0:07:17Well, it may seem odd, but just like us, trees have hormones.

0:07:17 > 0:07:20These chemical messengers flow through the body of the tree,

0:07:20 > 0:07:24controlling and managing all sorts of important processes.

0:07:24 > 0:07:28In us, these hormones are responsible for some of the biggest changes

0:07:28 > 0:07:31we'll go through in life, like pregnancy and puberty.

0:07:31 > 0:07:35In our tree, they're responsible for an equally crucial change.

0:07:37 > 0:07:40As autumn gets underway, driven by hormonal signals,

0:07:40 > 0:07:44trees begin to break down pigments and nutrients in their leaves

0:07:44 > 0:07:46to store over the winter.

0:07:51 > 0:07:53They begin to eat themselves.

0:07:57 > 0:08:01The result is a spectacular change in the colour of the leaves.

0:08:08 > 0:08:10Once the nutrients have been extracted,

0:08:10 > 0:08:14trees like our oak will start to shed their leaves to conserve water

0:08:14 > 0:08:16and energy in the coming months.

0:08:20 > 0:08:23But how exactly does our tree know

0:08:23 > 0:08:26when it's time to begin this huge change?

0:08:32 > 0:08:35For a very long time, people assumed changes in autumn

0:08:35 > 0:08:38were triggered simply by a drop in temperature.

0:08:39 > 0:08:43But what happens if there's an unusually cold spell in summer?

0:08:43 > 0:08:46How does our tree know not to drop all its leaves?

0:08:47 > 0:08:51It turns out that trees rely on a far more sophisticated method

0:08:51 > 0:08:55than temperature alone to sense the changing seasons.

0:08:56 > 0:08:58In their own way, they can SEE what's going on.

0:09:06 > 0:09:10Well, this should give you an idea of how most plants see the world.

0:09:10 > 0:09:13While you and I can perceive a wide range of colours,

0:09:13 > 0:09:16trees like our oak are only able to sense the red light

0:09:16 > 0:09:20in the spectrum and they can do this thanks to an incredible

0:09:20 > 0:09:22chemical pigment in their leaves called phytochrome.

0:09:26 > 0:09:29Phyocrome, a substance in our oak's leaf cells,

0:09:29 > 0:09:31is incredibly sensitive to the red light

0:09:31 > 0:09:34that makes up part of the sun's rays.

0:09:36 > 0:09:38It's a kind of chemical stopwatch

0:09:38 > 0:09:42that is also able to measure the hours of sunlight and darkness.

0:09:45 > 0:09:48So, as the nights get longer, the phytochrome acts like a signal,

0:09:48 > 0:09:51telling the tree that autumn has begun.

0:09:53 > 0:09:58This means that all the hormones that prepare the tree for the cold months

0:09:58 > 0:10:00kick in at exactly the right time.

0:10:05 > 0:10:09It's now October and our tree is not only dropping leaves,

0:10:09 > 0:10:14it's also time for our oak to release its most precious cargo.

0:10:14 > 0:10:18Autumn is not just a time for preparing for the cold,

0:10:18 > 0:10:23it's also when our oak releases its offspring out into the world.

0:10:23 > 0:10:25We're all familiar with acorns,

0:10:25 > 0:10:29but this really is a masterpiece of evolution.

0:10:29 > 0:10:33Inside this little capsule is not only the genetic code

0:10:33 > 0:10:36to make one of these, it also comes packed with food

0:10:36 > 0:10:38and protection from the elements,

0:10:38 > 0:10:42meaning this seed has all it needs to survive the winter.

0:10:43 > 0:10:47To spread acorns, the tree relies on the help of animals like jays

0:10:47 > 0:10:51and squirrels, who often store them underground

0:10:51 > 0:10:53and then forget where they are.

0:10:55 > 0:10:59But the oak has an ingenious trick to improve its acorn's chances.

0:10:59 > 0:11:05It varies the number of acorns it produces from year to year.

0:11:05 > 0:11:07Some years, there are thousands.

0:11:07 > 0:11:10Others, like this year, there are very few.

0:11:13 > 0:11:16While acorns are the perfect food for our friend here,

0:11:16 > 0:11:20the fact that she can't rely on oaks all the time

0:11:20 > 0:11:23means she has to find other sources of food.

0:11:23 > 0:11:27But every five or ten years, oaks have what is called a mast year.

0:11:27 > 0:11:29They produce such a deluge of acorns

0:11:29 > 0:11:32that all the acorn eaters simply can't cope -

0:11:32 > 0:11:35they're overwhelmed, no matter how hard they try.

0:11:35 > 0:11:40And this means that the chances of one acorn germinating

0:11:40 > 0:11:43and surviving becomes dramatically increased.

0:11:46 > 0:11:50With help from the local wildlife, at least one of our oak's acorns

0:11:50 > 0:11:54dropped this autumn is likely to germinate next year.

0:11:54 > 0:11:58And when it does, it will be a spectacular event.

0:12:04 > 0:12:07Fuelled by nutrients locked up within the acorn,

0:12:07 > 0:12:09our tree's offspring is brought to life.

0:12:25 > 0:12:28A shoot reaches upwards to find sunlight...

0:12:33 > 0:12:36..while a root penetrates beneath to find water.

0:12:52 > 0:12:55In just a few months,

0:12:55 > 0:12:59this acorn has developed into an infant oak with its very own leaves.

0:13:04 > 0:13:09This tiny organism is now able to fend for itself.

0:13:18 > 0:13:22The success of the oak is largely dependent on the animals

0:13:22 > 0:13:24that help disperse its acorns.

0:13:26 > 0:13:29And there's one species that, in the last 300 years,

0:13:29 > 0:13:31has been particularly helpful.

0:13:33 > 0:13:34And that's us.

0:13:35 > 0:13:37In the 18th and early 19th century,

0:13:37 > 0:13:40there was a frenzy of oak planting in Britain.

0:13:42 > 0:13:46In just six years, it was reported that one military officer

0:13:46 > 0:13:50managed to plant 922,000 oaks.

0:13:52 > 0:13:55The reason for this surge was simple -

0:13:55 > 0:13:57Britain had the world's most powerful navy

0:13:57 > 0:14:00and nearly all of our ships were made of oak.

0:14:04 > 0:14:06This is the HMS Victory,

0:14:06 > 0:14:11famous for defeating the French fleet at the Battle of Trafalgar.

0:14:12 > 0:14:18The ship is a product of almost 6,000 oak trees,

0:14:18 > 0:14:21reimagined by some of Britain's finest shipwrights.

0:14:25 > 0:14:27This vessel and hundreds like it

0:14:27 > 0:14:31were the reason for Britain's insatiable demand for oak.

0:14:35 > 0:14:39Climb inside and you see oak everywhere.

0:14:44 > 0:14:47This is the lower gun deck of the HMS Victory.

0:14:47 > 0:14:50Many of these sturdy oak timbers have been here

0:14:50 > 0:14:53since the ship first set sail in 1765.

0:14:54 > 0:14:59At night, hundreds of men would sleep jammed together in hammocks

0:14:59 > 0:15:02slung from oak beams and at meal times,

0:15:02 > 0:15:05they would eat together at these oak tables.

0:15:09 > 0:15:12For the crew of HMS Victory, oak surrounded them.

0:15:12 > 0:15:15It encased them and it kept them alive against the elements.

0:15:19 > 0:15:20The oak timbers of the Victory

0:15:20 > 0:15:24withstood the terrifying power of the sea.

0:15:31 > 0:15:35They managed to cross the Atlantic Ocean in hurricane season.

0:15:35 > 0:15:40They survived furious battles and innumerable volleys of cannon fire.

0:15:42 > 0:15:45They saw death and destruction on a colossal scale.

0:15:48 > 0:15:53And it was an oak hull that cradled Lord Nelson as he bled to death.

0:15:56 > 0:15:58Each of these spectacular oak planks

0:15:58 > 0:16:01has borne witness to and survived the many violent

0:16:01 > 0:16:05and dangerous battles on board HMS Victory, but this wood

0:16:05 > 0:16:09actually predates the building of this ship by hundreds of years.

0:16:09 > 0:16:13This wood is a product of medieval acorns that dropped all over Britain

0:16:13 > 0:16:18and, if you look closely, you can still see the story of their lives

0:16:18 > 0:16:20etched into the grain.

0:16:20 > 0:16:27The way oaks live, the battles they face in the natural world

0:16:27 > 0:16:32and their incredible adaptations are what makes this species

0:16:32 > 0:16:35so uniquely useful for building ships.

0:16:38 > 0:16:40The curved boughs of the oak,

0:16:40 > 0:16:45evolved to support the vast canopies of leaves,

0:16:45 > 0:16:48allow ships to be curved yet maintain the strength

0:16:48 > 0:16:51to withstand the full force of the ocean.

0:16:56 > 0:16:58By planting and cultivating oaks,

0:16:58 > 0:17:02humans have been able to travel between continents...

0:17:04 > 0:17:08..and spread our species to almost every corner of the planet.

0:17:11 > 0:17:14Harnessing the strength of this unique organism,

0:17:14 > 0:17:18we have been able to overcome even the most treacherous of oceans.

0:17:27 > 0:17:31Back at our tree, it's now late October and autumn is well underway.

0:17:31 > 0:17:34Our oak is now getting six hours less sunlight per day

0:17:34 > 0:17:38than it was in peak summer

0:17:38 > 0:17:41and, as the sun is the tree's only energy source,

0:17:41 > 0:17:46it must stock up and store resources for the winter.

0:17:46 > 0:17:51Crucial to how it does this is the tree's root system -

0:17:51 > 0:17:58a hidden subterranean world every bit as complex as the world above.

0:17:58 > 0:18:04I'm extremely keen to investigate how this works, but that's no easy task.

0:18:04 > 0:18:09Digging up our tree to see its roots would kill it, so to investigate,

0:18:09 > 0:18:14we're going to excavate the root system of an oak sapling...

0:18:14 > 0:18:16in its entirety.

0:18:19 > 0:18:22This is East Malling Research in Kent.

0:18:22 > 0:18:26For over 100 years, they have been experimenting with roots

0:18:26 > 0:18:30and plants to help develop better yields and they have given us

0:18:30 > 0:18:32a unique opportunity to get an insight

0:18:32 > 0:18:35into what's going on beneath the ground.

0:18:37 > 0:18:41The process begins by digging a metre-and-a-half deep trench.

0:18:42 > 0:18:46It's only then the REAL hard work can begin.

0:18:49 > 0:18:53An oak's root system, even a very young one like this,

0:18:53 > 0:18:55is incredibly complex and fragile

0:18:55 > 0:19:00and that means it can only be excavated by hand.

0:19:02 > 0:19:06We are trying to ensure that no root, no matter how small, is damaged.

0:19:07 > 0:19:11And that means the team must be meticulous in their work.

0:19:14 > 0:19:15It's a painstaking process

0:19:15 > 0:19:19that will take ten people almost two weeks to complete.

0:19:22 > 0:19:24But once it's done,

0:19:24 > 0:19:27we can begin to understand the subterranean world of the oak.

0:19:29 > 0:19:31Well, this is absolutely incredible.

0:19:31 > 0:19:34Look at how much soil they've had to remove

0:19:34 > 0:19:36to expose the root system of this tree.

0:19:36 > 0:19:39It's only 15 years old

0:19:39 > 0:19:43and several tonnes of earth have had to be shifted.

0:19:43 > 0:19:47This is something you'll never see in a month of Sundays

0:19:47 > 0:19:49and it's something I haven't seen ever before.

0:19:49 > 0:19:52But just look at the size of this, look how far they go out

0:19:52 > 0:19:55and as they go farther and farther out,

0:19:55 > 0:19:58these rootlets get finer and finer and finer

0:19:58 > 0:20:02until you're further out than the tree is tall, virtually.

0:20:05 > 0:20:09With the roots exposed, we can get a glimpse into their hidden world.

0:20:09 > 0:20:14Under extreme magnification, we can see these strange threads.

0:20:17 > 0:20:20They are known as mycorrhizal fungi.

0:20:20 > 0:20:22They grow all over the oak's roots

0:20:22 > 0:20:25and help them extract phosphates,

0:20:25 > 0:20:28a vital nutrient locked inside rocks in the soil.

0:20:32 > 0:20:36Now, I've just pulled out this little piece of rock here.

0:20:36 > 0:20:38I think I can see fungal threads

0:20:38 > 0:20:42that were actually attached onto this rock.

0:20:42 > 0:20:46Yes, so there's plant inaccessible phosphate in that rock

0:20:46 > 0:20:49and what the mychorriza do is they go inside of the rock

0:20:49 > 0:20:50and they pull out the phosphate

0:20:50 > 0:20:52and they can transport that then into the plant

0:20:52 > 0:20:54and into the root system,

0:20:54 > 0:20:56whereas the plant wouldn't be able to do that on its own.

0:20:56 > 0:21:00So the oak tree simply isn't able to access the phosphate

0:21:00 > 0:21:03in this without the fungi.

0:21:03 > 0:21:06No, it's much smaller and it can penetrate inside of the rock

0:21:06 > 0:21:09and take the nutrients back into the plant.

0:21:11 > 0:21:14The tips of the fungi can apply pressure

0:21:14 > 0:21:16equivalent to the inside of a car tyre.

0:21:18 > 0:21:20And this means they can physically penetrate

0:21:20 > 0:21:23parts of the rock to extract nutrients.

0:21:25 > 0:21:28These are the hidden helpers that allow oaks to get food

0:21:28 > 0:21:30from the most inaccessible of places.

0:21:33 > 0:21:34So, essentially,

0:21:34 > 0:21:38what we've got here is an oak tree like any other oak tree

0:21:38 > 0:21:45which is totally dependent on a vast army of microscopic fungal filaments,

0:21:45 > 0:21:48without which it wouldn't survive and it's a win-win for each of them,

0:21:48 > 0:21:51- they're helping each other.- They both require each other to survive.

0:21:51 > 0:21:54If you stretched out the root system of a mature plant,

0:21:54 > 0:21:59you would expect it to have about five miles of bare root system.

0:21:59 > 0:22:03However, if you then stretched out the mycorrhiza network,

0:22:03 > 0:22:07- that actually would spread around the entire world.- For a single tree?

0:22:07 > 0:22:13- For a single tree. - The more I see this system...

0:22:13 > 0:22:18Well, you know, what I thought of as a complex system is actually

0:22:18 > 0:22:21probably 100 times more complex.

0:22:25 > 0:22:28To see this root system in its full glory,

0:22:28 > 0:22:31we are going to take our sapling out of the ground.

0:22:34 > 0:22:38And put it on display in one of the outbuildings at East Malling.

0:22:52 > 0:22:55This is what an oak tree in autumn really looks like.

0:22:56 > 0:23:00At the top, we see leaves are being drained of their nutrients.

0:23:01 > 0:23:06Below, a vast branching lattice of roots, evolved to keep

0:23:06 > 0:23:10the tree standing and extract water and minerals from the soil.

0:23:13 > 0:23:16It is here that our oak will store much of its food

0:23:16 > 0:23:20over the winter months, but, laid out like this,

0:23:20 > 0:23:23the roots are not just beautiful,

0:23:23 > 0:23:26they also tell us a fascinating story.

0:23:28 > 0:23:31Now, Peter, to the untrained eye, this just

0:23:31 > 0:23:37looks like a tangle of roots, but you can tell a story about the tree now.

0:23:37 > 0:23:41I think we can because what we can see is a root, as you can see,

0:23:41 > 0:23:45going down here before it heads off out in that direction there

0:23:45 > 0:23:49and this is almost certainly the root that was inside the acorn

0:23:49 > 0:23:51and it's headed on down in this direction,

0:23:51 > 0:23:55it's grown on down and then, in the place that this was growing,

0:23:55 > 0:23:59we've got some rock underneath, some sandstone

0:23:59 > 0:24:03and this root has hit that rock and you can see, it's branched,

0:24:03 > 0:24:05it's sent out many branches to try and find

0:24:05 > 0:24:11a way around the obstacle and it's sent this one off in that direction.

0:24:12 > 0:24:16Beneath our oak at Wytham, the roots, like this sapling,

0:24:16 > 0:24:18will be a kind of map, showing the structure

0:24:18 > 0:24:21and composition of the earth in which they live.

0:24:23 > 0:24:24Within the forest,

0:24:24 > 0:24:28there's a very heterogeneous distribution of nutrients.

0:24:28 > 0:24:30It's not uniform

0:24:30 > 0:24:33and this particular tree has responded to that

0:24:33 > 0:24:36by producing this plethora of roots,

0:24:36 > 0:24:40this network of roots in this area, to fully exploit that resource.

0:24:40 > 0:24:44And presumably once that particular patch of resource here

0:24:44 > 0:24:47has been used up, it will just go away.

0:24:47 > 0:24:51Yes, these roots are ephemeral, they'll die off fairly quickly

0:24:51 > 0:24:54and the plant will invest its resources elsewhere

0:24:54 > 0:24:59- so it's a highly dynamic system. - It's not just fixed and immobile.

0:24:59 > 0:25:00No, absolutely not.

0:25:00 > 0:25:05What we are looking at here is something which is

0:25:05 > 0:25:08sensing its environment, responding to its environment

0:25:08 > 0:25:12and utilising resources in a very dynamic way.

0:25:20 > 0:25:25At 15 years old, this sapling has developed an amazing system of roots.

0:25:27 > 0:25:30Our tree at Wytham will have roots many times thicker,

0:25:30 > 0:25:33spreading out anywhere up to 30 metres from the trunk.

0:25:35 > 0:25:39It may seem excessive, but our tree will need them -

0:25:39 > 0:25:42not just for nutrients, but to keep itself standing.

0:25:47 > 0:25:49As its last leaves are finally shed,

0:25:49 > 0:25:54our oak is now fully prepared for the difficult conditions to come.

0:26:17 > 0:26:22As winter begins, our oak now enters its most perilous season.

0:26:28 > 0:26:31To survive, it has stripped itself of leaves,

0:26:31 > 0:26:36revealing an otherworldly beauty.

0:26:38 > 0:26:42Our tree needs to stay alive using almost no energy.

0:26:47 > 0:26:51But in this dormant state, our oak will have to face

0:26:51 > 0:26:56everything from gale force winds to sub-zero temperatures.

0:27:02 > 0:27:04Well, it's now the depths of winter.

0:27:04 > 0:27:08Our tree is bare and it's facing some of the harshest conditions

0:27:08 > 0:27:10it will have to endure all year.

0:27:10 > 0:27:13At night, the temperature's going to drop well below freezing

0:27:13 > 0:27:15and out of the shelter of the forest,

0:27:15 > 0:27:18the winds are going to be hitting the top of this tree at full force.

0:27:18 > 0:27:21To get some idea of what the tree experiences,

0:27:21 > 0:27:24I'm going to be sleeping - or trying to sleep -

0:27:24 > 0:27:2640 feet up there.

0:27:27 > 0:27:31While our tree looks lifeless in winter, oaks provide a home

0:27:31 > 0:27:37to species ranging from spiders and woodlice to bats and owls.

0:27:37 > 0:27:39They all utilise the great size

0:27:39 > 0:27:42and stability of the oak to provide shelter.

0:27:45 > 0:27:48A tree is not just a tree - it's a home.

0:27:49 > 0:27:52I think you'll be warm enough going up there.

0:27:52 > 0:27:55'I've always wanted to experience what it might be like

0:27:55 > 0:27:59'to live in an oak tree and now I'm finally getting a chance,

0:27:59 > 0:28:01'even if it is just for one night.

0:28:10 > 0:28:13'Getting up to my perch is no mean feat,

0:28:13 > 0:28:15'but it gives me a totally new perspective.'

0:28:16 > 0:28:18Yes, it feels good!

0:28:25 > 0:28:30Once I'm safely ensconced, it's time to try and get some sleep.

0:28:32 > 0:28:35I'll have a look out.

0:28:35 > 0:28:39'At this height, you get a sense of how big a space this really is.

0:28:39 > 0:28:43'For a hibernating bat or nesting owl,

0:28:43 > 0:28:47'our oak will provide everything they need to stay safe over the winter.

0:28:51 > 0:28:54'But for me, sleep is not coming easily.'

0:28:54 > 0:28:56OWL HOOTS

0:28:56 > 0:29:00I did hear a couple of noises earlier,

0:29:00 > 0:29:05which I thought might have been deer or...

0:29:07 > 0:29:09I'm sure I heard a fox.

0:29:13 > 0:29:17Well, it's about three o'clock in the morning and it's pretty cool.

0:29:17 > 0:29:23It's just under three degrees and I'm toasty in my sleeping bag here.

0:29:23 > 0:29:26I've got these layers of down and that really insulates me

0:29:26 > 0:29:30pretty effectively from the cold and that is working pretty much

0:29:30 > 0:29:33like the bark of the oak tree, which is an effective insulator.

0:29:35 > 0:29:39The same principle that is keeping me warm is also keeping our oak

0:29:39 > 0:29:42and its inhabitants warm.

0:29:42 > 0:29:44Its thick bark is acting like a blanket.

0:29:47 > 0:29:51But temperatures in winter can drop below minus ten

0:29:51 > 0:29:54and, in those conditions, the bark is not enough.

0:29:54 > 0:29:57CRUNCHING AND RUSTLING

0:29:57 > 0:30:00Because water expands as it freezes,

0:30:00 > 0:30:03if our oak were actually to freeze solid in winter,

0:30:03 > 0:30:06it could cause catastrophic damage.

0:30:07 > 0:30:11So the oak has an additional strategy.

0:30:11 > 0:30:15In the lead up to winter, it withdraws some of the fluid

0:30:15 > 0:30:18from its delicate living cells.

0:30:18 > 0:30:19It dehydrates itself.

0:30:21 > 0:30:25What liquid is left contains high concentrations of sugars

0:30:25 > 0:30:27that act as a kind of antifreeze.

0:30:31 > 0:30:35It is what allows our oak to survive not just one cold night,

0:30:35 > 0:30:38but many tens of thousands of them.

0:30:44 > 0:30:48Well, I came up at night, last night, in the dark.

0:30:48 > 0:30:54And it is now apparent just quite how high I am off the ground.

0:30:54 > 0:30:57Thankfully, for me, it was a pretty still night.

0:30:57 > 0:30:59It's cold, but it's not windy.

0:30:59 > 0:31:02And the view you get from here is certainly worth it.

0:31:02 > 0:31:08But it does give me an absolutely unique experience

0:31:08 > 0:31:10of life in an oak tree.

0:31:15 > 0:31:19From up here you really begin to appreciate the scale of our tree.

0:31:19 > 0:31:21It is a huge habitat.

0:31:21 > 0:31:25In the winter, while our tree might look lifeless,

0:31:25 > 0:31:29it is actually a vital part of the ecosystem at Wytham.

0:31:30 > 0:31:32Our oak is crucial to the survival

0:31:32 > 0:31:36of countless thousands of insects and other animals

0:31:36 > 0:31:38over the inhospitable winter months.

0:31:45 > 0:31:47It is now mid-January

0:31:47 > 0:31:50and we are going to take a new and very different

0:31:50 > 0:31:51digital scan of our tree.

0:31:51 > 0:31:56By imaging the tree without its leaves in these still conditions

0:31:56 > 0:31:59we should be able to get a much more accurate estimate

0:31:59 > 0:32:03of the weight of our oak's wood, and this will be essential

0:32:03 > 0:32:07to understanding how the tree changes over the year.

0:32:07 > 0:32:10Dr Eric Casella from the Forestry Commission

0:32:10 > 0:32:11is braving the cold for us.

0:32:11 > 0:32:13And the model he is creating

0:32:13 > 0:32:16will allow us to see our tree in a totally new way.

0:32:23 > 0:32:27Eric's scan reveals the sheer complexity of our oak.

0:32:29 > 0:32:32Using this model we can work out

0:32:32 > 0:32:36that our tree is made up of almost 10 tons of wood.

0:32:36 > 0:32:38But the scan also reveals more.

0:32:38 > 0:32:42Its branches are distinctly clustered to one side of the tree.

0:32:44 > 0:32:47Our oak has directed the growth of its branches

0:32:47 > 0:32:49away from the side shaded by the forest

0:32:49 > 0:32:53and towards the area that receives most sunlight.

0:32:53 > 0:32:57It has uniquely optimised its shape to suit its position.

0:32:58 > 0:33:01But this phenomenon is not just above ground.

0:33:01 > 0:33:05An oak's root system adapts to help them stay standing in winter.

0:33:06 > 0:33:09To see how this works, I want to try something

0:33:09 > 0:33:11that has never been done before,

0:33:11 > 0:33:14I want to simulate the effects of gale force winds

0:33:14 > 0:33:16on an oak.

0:33:16 > 0:33:21This is a Forestry Commission research site just outside Edinburgh

0:33:21 > 0:33:23and here they are doing pioneering work

0:33:23 > 0:33:28examining the strength and stability of many different tree species.

0:33:29 > 0:33:31They have allowed me in for the afternoon

0:33:31 > 0:33:33to come and watch one of their experiments.

0:33:35 > 0:33:36Today, for the first time,

0:33:36 > 0:33:40they are going to study how an oak tree behaves during a storm.

0:33:42 > 0:33:44Some people might be a little bit shocked

0:33:44 > 0:33:48that you are just about pull down a perfectly healthy oak tree.

0:33:48 > 0:33:50What is the reason for doing it?

0:33:50 > 0:33:52Well, one of the reasons that we do this is to assess

0:33:52 > 0:33:54the stability of trees and forests,

0:33:54 > 0:33:57without doing this we don't know

0:33:57 > 0:33:59what happens when a storm hits.

0:33:59 > 0:34:01You're trying to simulate the sort of forces

0:34:01 > 0:34:04that that tree would experience in a high wind?

0:34:04 > 0:34:06Exactly.

0:34:06 > 0:34:09Before we pull it, the tree must be rigged with sensors

0:34:09 > 0:34:13to monitor exactly how it behaves under stress.

0:34:13 > 0:34:17Once everything is set it is time to get back to a safe distance

0:34:17 > 0:34:18and begin the pull.

0:34:18 > 0:34:21MACHINERY WHIRS

0:34:32 > 0:34:34It is going.

0:34:40 > 0:34:42Certainly going.

0:34:55 > 0:34:57Beautiful.

0:35:02 > 0:35:06With the tree down, Paul and his team can now analyse the results.

0:35:08 > 0:35:14At what angle did the tree suddenly become sufficiently, you know,

0:35:14 > 0:35:17tipped over, that it fell on its own?

0:35:17 > 0:35:19Well, in this case it was only six degrees.

0:35:19 > 0:35:23- That is nothing, that is like that... - That is correct, yeah.

0:35:23 > 0:35:28So that tree, actually, it has got very shallow roots,

0:35:28 > 0:35:29it is not very big.

0:35:29 > 0:35:31No. That is exactly what it is.

0:35:31 > 0:35:35You can see, when we looked at the roots, that it was very shallow.

0:35:35 > 0:35:39While at first glance it may seem this oak came down quite easily,

0:35:39 > 0:35:41it would have taken a force 10 storm

0:35:41 > 0:35:44to produce the same effect as Paul's winch.

0:35:45 > 0:35:49That size of storm can produce 12-metre waves at sea

0:35:49 > 0:35:51and has gusts of wind anywhere up to 90mph.

0:35:54 > 0:35:58This oak was, in fact, amazingly stable given its relatively shallow roots.

0:36:00 > 0:36:03It is likely our oak has grown much deeper roots

0:36:03 > 0:36:06and with its huge spread of branches

0:36:06 > 0:36:09it is able to dissipate the force of the winds

0:36:09 > 0:36:10much more effectively.

0:36:10 > 0:36:15It means that our tree can withstand much harsher conditions.

0:36:16 > 0:36:20That a large, heavy structure like our oak can remain standing

0:36:20 > 0:36:25over 400 winters is a remarkable feat of evolutionary engineering.

0:36:26 > 0:36:29And much of what has made it so successful

0:36:29 > 0:36:32at surviving the cold and the storms of winter

0:36:32 > 0:36:34has also made it useful to us.

0:36:41 > 0:36:45For thousands of years, oak has been an essential building material.

0:36:47 > 0:36:51By slicing and shaping trunks of oak into regular lengths

0:36:51 > 0:36:54we are able to build all manner of shelters

0:36:54 > 0:36:56to protect us from the elements.

0:37:03 > 0:37:05In the harsh winter months, oak timbered houses

0:37:05 > 0:37:08have kept us safe for centuries.

0:37:09 > 0:37:11And thanks to the durability of the wood,

0:37:11 > 0:37:15many of these incredibly old buildings still endure today.

0:37:17 > 0:37:20But there is perhaps one building above any other

0:37:20 > 0:37:24that showcases the extraordinary properties of oak timbers,

0:37:24 > 0:37:27and just what they can help us create.

0:37:30 > 0:37:32Built in the 13th century,

0:37:32 > 0:37:36it remains one of the most imposing and impressive structures

0:37:36 > 0:37:37in the British Isles.

0:37:39 > 0:37:41And at its heart is oak.

0:37:58 > 0:38:00This is Salisbury Cathedral.

0:38:00 > 0:38:04It is one of the masterpieces of British medieval architecture.

0:38:04 > 0:38:06Looking at its size and scale

0:38:06 > 0:38:10it is hard to believe this building was created almost 800 years ago

0:38:10 > 0:38:13and throughout its incredible structure,

0:38:13 > 0:38:15everywhere you look, oak has been put to use.

0:38:19 > 0:38:21During its construction,

0:38:21 > 0:38:25an incredible 2,641 tonnes of oak

0:38:25 > 0:38:29were employed to help build the cathedral.

0:38:36 > 0:38:40But it is not until you ascend above the vaulted plaster ceilings

0:38:40 > 0:38:42that you can really understand

0:38:42 > 0:38:45how important this single species of tree has been.

0:38:59 > 0:39:03This building has within it whole forests

0:39:03 > 0:39:06reimagined and remoulded by human hands.

0:39:18 > 0:39:21Now, these oak beams have been here for a very long time.

0:39:21 > 0:39:25In fact these are among the oldest of the oak beams here.

0:39:25 > 0:39:29Yes, the area we are in now is 13th century timber.

0:39:29 > 0:39:35It has been tested, and it was felled in the spring of 1222.

0:39:39 > 0:39:42The roof here can be dated so precisely

0:39:42 > 0:39:45thanks to patterns in the wood.

0:39:47 > 0:39:51As an oak grows it makes large amounts of new tissue in the spring,

0:39:51 > 0:39:57followed by a much smaller amount of denser wood later in the year.

0:39:57 > 0:40:01This rapid, then slow, growth gives the appearance of rings.

0:40:02 > 0:40:06If the summer weather is good, a tree will grow a much wider ring

0:40:06 > 0:40:12and that gives us a tantalising snapshot of the past and its climate.

0:40:13 > 0:40:17By looking at similar patterns across many different samples

0:40:17 > 0:40:21it is possible to date pieces of oak with extreme precision.

0:40:21 > 0:40:25It is even possible to tell where an individual oak tree was growing.

0:40:27 > 0:40:29And it turns out, to build this amazing roof

0:40:29 > 0:40:35the local craftsmen used oak from as far afield as Ireland.

0:40:35 > 0:40:38These two don't look quite the same, to me.

0:40:38 > 0:40:43No, if you look at the rings, closely, this is Irish oak.

0:40:43 > 0:40:46The tree rings are really tight together

0:40:46 > 0:40:50because the summer and the winter almost blend into one another.

0:40:50 > 0:40:52English oak, they have hotter summers,

0:40:52 > 0:40:55so they have a better growth rate during the summer.

0:40:55 > 0:40:59It makes it stronger, it is also slightly lighter as well.

0:40:59 > 0:41:02Which, when you are putting thousands of tonnes of oak

0:41:02 > 0:41:05into a roof structure, that helps.

0:41:05 > 0:41:08It all adds up. Yeah.

0:41:09 > 0:41:13With Salisbury's spectacular roof completed

0:41:13 > 0:41:17its builders decided to add one extraordinary feature.

0:41:19 > 0:41:20A monumental spire,

0:41:20 > 0:41:23that must have filled the medieval population

0:41:23 > 0:41:26in the surrounding area with absolute awe.

0:41:28 > 0:41:32Today it still remains the largest spire in the UK.

0:41:33 > 0:41:38And inside is an incredible lattice of oak timbers.

0:41:42 > 0:41:45I tell you, if you didn't like heights,

0:41:45 > 0:41:48this would be not much fun for somebody.

0:41:48 > 0:41:52This is quite an amazing feat of engineering, really.

0:41:52 > 0:41:54And it was essentially an afterthought,

0:41:54 > 0:41:56after the cathedral was built,

0:41:56 > 0:41:59and they have had to do this ingenious framework

0:41:59 > 0:42:01to help them build it.

0:42:01 > 0:42:03Yeah, a thousand people were working on it,

0:42:03 > 0:42:06they were doing it to get closer to God, if you like,

0:42:06 > 0:42:11so it was their vocation, their way of life, to be closer to heaven.

0:42:11 > 0:42:14You just look up and marvel, and you almost think,

0:42:14 > 0:42:16it is divine intervention, really.

0:42:16 > 0:42:21It is probably one of the most amazing structures I have ever seen.

0:42:36 > 0:42:40Well, you do get an amazing sense of the countryside from up here.

0:42:40 > 0:42:44But don't forget, it is the oak forests growing down there,

0:42:44 > 0:42:46the fact that they can withstand

0:42:46 > 0:42:48all that the weather has to throw at them,

0:42:48 > 0:42:50even in the harshest winter,

0:42:50 > 0:42:53and the strength and durability and resilience

0:42:53 > 0:42:54of the wood that they gave,

0:42:54 > 0:42:57that made structures like this possible at all.

0:43:01 > 0:43:04Oak is an incredible building material.

0:43:04 > 0:43:07But even today we have yet to come anywhere close

0:43:07 > 0:43:11to creating structures with the economy and beauty

0:43:11 > 0:43:13of the oak tree in its natural form.

0:43:22 > 0:43:27As the winter deepens and temperatures drop down below freezing,

0:43:27 > 0:43:30our oak structure will really be put to the test.

0:43:30 > 0:43:34I want to find out exactly how healthy our oak is

0:43:34 > 0:43:37and how many more winters like this it might be able to endure.

0:43:42 > 0:43:44Thanks to some ingenious new technology,

0:43:44 > 0:43:48we now have the power to look inside it and find out.

0:43:48 > 0:43:52This is very similar to the MRI scanner that we use of the body,

0:43:52 > 0:43:54so it takes slices through the body,

0:43:54 > 0:43:56we take slices through the tree,

0:43:56 > 0:44:00and we're just trying to determine whether the wood is sound or not.

0:44:00 > 0:44:03As electrical currents are passed through the tree

0:44:03 > 0:44:08a map is created that will reveal the internal structure of our oak.

0:44:08 > 0:44:11Well, there is the image. What does that show us?

0:44:11 > 0:44:13Well, what it is showing us is

0:44:13 > 0:44:15we have wet and dry areas, basically, George.

0:44:15 > 0:44:17And the dry areas are in red,

0:44:17 > 0:44:19some of them are around the outside of the stem,

0:44:19 > 0:44:21the bulk of the stem in the middle, is blue,

0:44:21 > 0:44:23but there are breaks in that,

0:44:23 > 0:44:25and that suggests there's something wrong

0:44:25 > 0:44:28with the inside of the stem, it is not a natural picture.

0:44:28 > 0:44:33Clearly something has happened, we need to investigate that further.

0:44:33 > 0:44:37This tiny gap between the roots of our oak may look unremarkable

0:44:37 > 0:44:40but inside is a hidden world.

0:44:40 > 0:44:43Let's get this into position so you can see.

0:44:43 > 0:44:45That is quite a big hole, isn't it?

0:44:45 > 0:44:48And we can see all that decayed wood.

0:44:48 > 0:44:50So we have got a very, very large cavity

0:44:50 > 0:44:52where the heart wood is missing,

0:44:52 > 0:44:54and we can see fingers of wood hanging down,

0:44:54 > 0:44:57where the fungus has rotted out the wood between it.

0:44:57 > 0:45:00We call it the Eiffel Tower fungus.

0:45:00 > 0:45:03It really only affects the lower part of the stem

0:45:03 > 0:45:05and leaves the tree effectively standing

0:45:05 > 0:45:06on its buttresses, like this,

0:45:06 > 0:45:08a bit like the Eiffel Tower on its four legs...

0:45:08 > 0:45:12- Hence the name.- We've got multiple legs, hence the name.

0:45:12 > 0:45:14Even though that is quite a big hole

0:45:14 > 0:45:18it is clearly not having a hugely harmful effect on the tree,

0:45:18 > 0:45:20it is still here, it's still growing.

0:45:20 > 0:45:23Absolutely, it has still got these feet in the ground,

0:45:23 > 0:45:26if you like, it can still draw up nutrients and water,

0:45:26 > 0:45:28and give it a firm footing in the ground,

0:45:28 > 0:45:30even though the heart is gone,

0:45:30 > 0:45:33and it could still be there in another 500 years.

0:45:35 > 0:45:38It is likely our oak will still be standing here,

0:45:38 > 0:45:42alive and growing in the landscape of the 26th century.

0:45:45 > 0:45:48But after this vast span of time has passed,

0:45:48 > 0:45:51the fungus eating away at our tree's inside,

0:45:51 > 0:45:52and the age of its wood,

0:45:52 > 0:45:54will mean it looks quite different.

0:45:57 > 0:46:00Scattered across the UK are a select few oaks

0:46:00 > 0:46:03that have survived over a thousand years.

0:46:03 > 0:46:07And they give us clues about our tree's ultimate fate.

0:46:16 > 0:46:19This is the Bowthorpe Oak in Lincolnshire.

0:46:19 > 0:46:22And over the last one thousand years,

0:46:22 > 0:46:26its insides have been almost entirely hollowed out by fungus.

0:46:36 > 0:46:39Each valley, ridge, and peak in its wood

0:46:39 > 0:46:43tells the story of the battles this tree has faced.

0:46:49 > 0:46:53Ravaged by the bitter cold of a thousand winters,

0:46:53 > 0:46:57its bark looks like the surface of an alien world.

0:47:05 > 0:47:08Sculpted by huge passages of time.

0:47:43 > 0:47:48The Bowthorpe Oak is a window into our tree's distant future.

0:47:51 > 0:47:54But for now our tree is thriving.

0:47:54 > 0:47:57It has endured everything the winter has thrown at it

0:47:57 > 0:48:01and is ready and waiting to once again come to life.

0:48:16 > 0:48:19As the temperature warms and the forest is bathed in sunlight,

0:48:19 > 0:48:23the countless plants and animals in Wytham Woods come to life.

0:48:27 > 0:48:33Once again, the forest is reborn with colour, movement, and life.

0:48:39 > 0:48:43And for our oak, this will be the season of most dramatic growth.

0:48:45 > 0:48:49After many months in a state of suspended animation,

0:48:49 > 0:48:51our oak is beginning to come to life.

0:48:51 > 0:48:53The buds are finally starting to burst

0:48:53 > 0:48:56and our tree is about to undergo

0:48:56 > 0:48:59one of the most dramatic changes of the year.

0:48:59 > 0:49:03In the next few weeks, this oak is going to have an epic growth spurt.

0:49:07 > 0:49:09To capture this transformation,

0:49:09 > 0:49:11we are setting up two specially designed cameras.

0:49:13 > 0:49:18Bolted to the spot, they will take over 100 pictures each day,

0:49:18 > 0:49:21and allow us to compress this spectacular event

0:49:21 > 0:49:23into a timescale we can appreciate.

0:49:26 > 0:49:30Just like our tree, the cameras will be powered by the sun

0:49:30 > 0:49:35and will capture images continuously for the next six months.

0:49:35 > 0:49:38With everything set, the cameras are started.

0:49:47 > 0:49:49As winter ends and spring begins,

0:49:49 > 0:49:54over 700,000 individual leaves emerge across our oak.

0:50:00 > 0:50:01It is a truly astonishing change.

0:50:17 > 0:50:21This remarkable transformation needs huge amounts of water.

0:50:21 > 0:50:24Hidden from the naked eye,

0:50:24 > 0:50:28at its peak, our tree will be pumping 70kg of water each hour

0:50:28 > 0:50:29out of the ground.

0:50:31 > 0:50:35By looking at the oak wood just beneath the bark with a microscope,

0:50:35 > 0:50:39we can see how this huge quantity of water gets moved around the tree.

0:50:41 > 0:50:44These intricate pipes are known as the xylem vessels

0:50:44 > 0:50:47and they run through a layer known as the cambium,

0:50:47 > 0:50:50that carries water upwards, from the roots to the leaves.

0:50:53 > 0:50:55And thanks to some ingenious technology,

0:50:55 > 0:50:59we can now measure exactly how much fluid is moving through them.

0:51:02 > 0:51:03With the help of Dr Lucy Rowland,

0:51:03 > 0:51:07I'm going to set up an experiment that I hope will reveal

0:51:07 > 0:51:09exactly how much water our tree is taking up

0:51:09 > 0:51:13and how this changes over the spring.

0:51:13 > 0:51:15This is a sap flow monitor.

0:51:15 > 0:51:19And as water travels up the xylem tissue, these probes heat it up.

0:51:20 > 0:51:24By measuring how quickly this heat is carried away,

0:51:24 > 0:51:27the device can calculate how much water is flowing

0:51:27 > 0:51:29through the trunk of the tree.

0:51:29 > 0:51:31Over 24 hours of measurements,

0:51:31 > 0:51:36we see our tree's water consumption varies dramatically.

0:51:36 > 0:51:39This is at night when we don't have sap flowing up in the tree.

0:51:39 > 0:51:43And this peak here, this is lunchtime-ish yesterday,

0:51:43 > 0:51:47when we had maximum flow up through the stem of the tree.

0:51:47 > 0:51:53And you can see here that we have got about 10kg of water per hour,

0:51:53 > 0:51:56yesterday lunchtime, going up through the tree.

0:51:56 > 0:52:00And that will increase as the leaf area of the tree increases?

0:52:00 > 0:52:03Yes, so the more leaves that come out on this oak

0:52:03 > 0:52:05over the next few weeks,

0:52:05 > 0:52:08the bigger that this peak is going to be.

0:52:10 > 0:52:13As we move through the next two weeks of spring,

0:52:13 > 0:52:16our tree begins to consume ever more water in the middle of the day.

0:52:20 > 0:52:23It reaches a peak of over 60kg of water an hour,

0:52:23 > 0:52:24as more and more leaves emerge.

0:52:32 > 0:52:35But leaves are not all our tree is now producing.

0:52:36 > 0:52:38It is now late April

0:52:38 > 0:52:42and for a precious few weeks, our oak grows these strange new structures.

0:52:43 > 0:52:46Their role is to ensure the future of our tree,

0:52:46 > 0:52:49and the continuing success of the oak.

0:52:51 > 0:52:54These fragile little objects are known as catkins.

0:52:54 > 0:52:56And they are oak's male flower,

0:52:56 > 0:52:59and it is the appearance of these every spring

0:52:59 > 0:53:02that signals the start of the oak's reproductive cycle.

0:53:02 > 0:53:05And if you look carefully inside each of these little blobs,

0:53:05 > 0:53:09you will find it is completely packed with grains of pollen.

0:53:11 > 0:53:15But these pollen grains are only half the story.

0:53:15 > 0:53:18Our oak will also produce a female flower,

0:53:18 > 0:53:20but not until later in the spring.

0:53:20 > 0:53:22It means that these pollen grains

0:53:22 > 0:53:25will need to find a female oak flower on another tree,

0:53:25 > 0:53:27if they want to pollinate.

0:53:27 > 0:53:30And that means taking to the skies.

0:53:36 > 0:53:38In spring, an oak tree like ours

0:53:38 > 0:53:42can release up to two billion individual particles of pollen.

0:53:42 > 0:53:47And inside each one of these tiny grains is the unique DNA of our tree.

0:53:47 > 0:53:50Blown around by the wind, they can spread for miles,

0:53:50 > 0:53:52but their mission is simple,

0:53:52 > 0:53:56each grain is seeking a chance encounter with a female flower

0:53:56 > 0:54:00of one of the other 5,000 oak trees in the surrounding woods.

0:54:04 > 0:54:06Filling the air above the forest,

0:54:06 > 0:54:09billions of our oak's individual pollen grains

0:54:09 > 0:54:11are scattered by the spring breeze.

0:54:18 > 0:54:23Up close, we can see how complex this tiny vessel really is.

0:54:23 > 0:54:27A thick, warty shell protects the delicate genetic cargo inside,

0:54:27 > 0:54:30as gusts of wind carry it for miles.

0:54:35 > 0:54:38This is the target of our oak's pollen grains.

0:54:38 > 0:54:40A female oak flower.

0:54:45 > 0:54:49If the pollen is lucky enough to land here, it will fertilise the flower.

0:54:49 > 0:54:51And over the next few months,

0:54:51 > 0:54:56the female oak flower will combine its genetic material with the pollen

0:54:56 > 0:54:58to create a tiny acorn.

0:54:58 > 0:55:00A descendant of our oak.

0:55:09 > 0:55:11The yearly act of pollination

0:55:11 > 0:55:14is crucial for the long-term future of the oak.

0:55:14 > 0:55:17But at Wytham, they have been using pollen

0:55:17 > 0:55:20to open up a unique window into its past.

0:55:20 > 0:55:21This is Marley Fen.

0:55:21 > 0:55:23It is an area of Wytham Woods

0:55:23 > 0:55:26that has remained largely unchanged for thousands of years.

0:55:26 > 0:55:28And over that time,

0:55:28 > 0:55:30as plants and trees reproduce every spring,

0:55:30 > 0:55:34the air is filled with trillions and trillions of pollen grains

0:55:34 > 0:55:37that eventually end up in this peat here.

0:55:38 > 0:55:41As pollen settles on the surface of the fen,

0:55:41 > 0:55:44plants, leaves, and other biological matter

0:55:44 > 0:55:47gradually build up on top of it.

0:55:47 > 0:55:52Over time, layer upon layer of pollen becomes preserved within the soil.

0:55:52 > 0:55:56Inside this somewhat unremarkable looking mud,

0:55:56 > 0:55:59an incredible story has been preserved,

0:55:59 > 0:56:00one that records in detail

0:56:00 > 0:56:04the ebb and flow of various trees and plants in the area

0:56:04 > 0:56:06for the last 12,000 years.

0:56:06 > 0:56:12But to uncover the story hidden in here, you have to dig down.

0:56:12 > 0:56:14And that is what Dr Helen Walkington and her team

0:56:14 > 0:56:16have been doing for the last ten years.

0:56:19 > 0:56:21They use a long metal tube

0:56:21 > 0:56:24to extract thin cylinders of peat from the fen.

0:56:28 > 0:56:29This four metre long core

0:56:29 > 0:56:33can tell scientists how the landscape and vegetation in Wytham Woods

0:56:33 > 0:56:36has changed since the end of the last ice age.

0:56:43 > 0:56:47This soil, from four metres down, was on the surface 12,000 years ago,

0:56:47 > 0:56:51and shows Britain then was a cold and barren place.

0:56:54 > 0:56:56So we have got here clay-rich material

0:56:56 > 0:57:00with lots of iron and fragments of rock.

0:57:00 > 0:57:02So, I don't know if you can see here,

0:57:02 > 0:57:04but there are rock fragments within it,

0:57:04 > 0:57:07so it tells us there was lots of erosion in this landscape,

0:57:07 > 0:57:12and that's how we know that there was not much vegetation at the time.

0:57:12 > 0:57:14Without plant roots to hold the soil in place,

0:57:14 > 0:57:18the landscape of Britain after the last ice age

0:57:18 > 0:57:19was prone to rapid changes.

0:57:20 > 0:57:23But as we move along the core,

0:57:23 > 0:57:26more and more pollen begins appearing

0:57:26 > 0:57:29as plants of all kind take hold.

0:57:29 > 0:57:32As the climate warmed, it meant oak was able to move north

0:57:32 > 0:57:36and 9,000 years ago its pollen appeared

0:57:36 > 0:57:38for the first time at Wytham.

0:57:38 > 0:57:41This material would represent organic matter

0:57:41 > 0:57:46that would have been moved into Marley Fen 9,000 years ago

0:57:46 > 0:57:47and at the same time,

0:57:47 > 0:57:50oak pollen would be blowing around in the atmosphere

0:57:50 > 0:57:52and would settle out on the surface,

0:57:52 > 0:57:56and gradually all the material in the rest of the core

0:57:56 > 0:57:58would be on top and pushed down.

0:57:58 > 0:57:59I find it incredible

0:57:59 > 0:58:03that I can actually put my finger on that piece of core

0:58:03 > 0:58:06and touch the exact part of the history of Wytham

0:58:06 > 0:58:08where oaks came in.

0:58:08 > 0:58:099,000 years ago.

0:58:09 > 0:58:149,000 years ago, and I can actually physically connect with that.

0:58:14 > 0:58:17And what are humans doing at this time?

0:58:17 > 0:58:20At this time, we don't have humans at this point.

0:58:20 > 0:58:22So this is it, this is pristine?

0:58:22 > 0:58:26Once the humans do come into the landscape,

0:58:26 > 0:58:28things start changing very quickly.

0:58:29 > 0:58:33Moving through the core to nearly 2,000 years ago,

0:58:33 > 0:58:35cereal grains begin to appear at Wytham,

0:58:35 > 0:58:39and this signals a new type of human activity.

0:58:40 > 0:58:42Cereal grains are brought in by the Romans,

0:58:42 > 0:58:45and they need to completely clear the landscape

0:58:45 > 0:58:48to make space for fields, to cultivate them.

0:58:48 > 0:58:51The cereals, we don't know the exact type of cereal they were growing,

0:58:51 > 0:58:54because the shape of the pollen grains does not unlock that for us

0:58:54 > 0:58:56like it does for the trees,

0:58:56 > 0:58:58which we can get down to the species level.

0:58:58 > 0:59:03But certainly the Romans would be using this landscape to grow food,

0:59:03 > 0:59:07and then as we progress up the core,

0:59:07 > 0:59:10we find that oak becomes less dominant.

0:59:10 > 0:59:12But it is still here.

0:59:12 > 0:59:15It is still present, but it becomes less dominant.

0:59:15 > 0:59:19And that is because humans have set about clearing these landscapes

0:59:19 > 0:59:21on a much, much greater scale.

0:59:21 > 0:59:25The oak tree that we are filming in Wytham Woods

0:59:25 > 0:59:28is going to be going somewhere about here.

0:59:28 > 0:59:31Yeah, it was probably an acorn around 0.7 metres,

0:59:31 > 0:59:33something like that.

0:59:33 > 0:59:35And so that represents the period of time

0:59:35 > 0:59:38that your oak tree has been growing.

0:59:38 > 0:59:43Well, at least it shows that things change over time.

0:59:43 > 0:59:47And there have been huge, huge changes in 12,000 years,

0:59:47 > 0:59:50which is a very short piece of earth's history.

0:59:50 > 0:59:52Absolutely, and in 12,000 years

0:59:52 > 0:59:56those changes have been natural and human induced.

0:59:56 > 1:00:00There is a kind of interplay of those at this site.

1:00:00 > 1:00:03And I am sure that in the next thousand years

1:00:03 > 1:00:05that will be the case as well.

1:00:05 > 1:00:07The oak's pollen offers us

1:00:07 > 1:00:12a vivid glimpse of the challenges trees face over vast spans of time.

1:00:13 > 1:00:16But, right now, our tree is gearing up to face

1:00:16 > 1:00:18a much more imminent danger.

1:00:27 > 1:00:30It's now late May, and our tree is in full leaf.

1:00:31 > 1:00:33The oak boughs visibly droop with

1:00:33 > 1:00:36the weight of the new material they have to support.

1:00:38 > 1:00:42But this abundance of young, soft leaves are extremely vulnerable.

1:00:42 > 1:00:44A great threat is now emerging

1:00:44 > 1:00:49and our tree must react quickly if it wants to survive.

1:00:49 > 1:00:51This is the lava of the winter moth.

1:00:51 > 1:00:53It may not look very much,

1:00:53 > 1:00:56but this is one of the oak's most fearsome enemies.

1:00:56 > 1:00:59This little chap will eat an incredible amount of food

1:00:59 > 1:01:01to become adult.

1:01:01 > 1:01:05In fact, it will eat up to 27,000 times its own weight in young

1:01:05 > 1:01:09oak leaves and, right now, there are countless thousands of these

1:01:09 > 1:01:12caterpillars infesting our tree.

1:01:12 > 1:01:15But our oak isn't powerless in the face of this attack.

1:01:18 > 1:01:22After the oak's new leaves first emerge, for a short while,

1:01:22 > 1:01:26the winter moth caterpillars, amongst others, will gorge themselves.

1:01:27 > 1:01:29Unprotected from these attackers,

1:01:29 > 1:01:35our oak would struggle to survive the summer, but, incredibly,

1:01:35 > 1:01:40our tree is able to recognise exactly what's happening to it and respond.

1:01:46 > 1:01:49Professor Sue Hartley has spent much of her career

1:01:49 > 1:01:53looking at the ways plants defend themselves against insect attacks,

1:01:53 > 1:01:56and was one of the first to recognise just how sophisticated

1:01:56 > 1:01:59trees like our oak really are.

1:02:00 > 1:02:04How does an oak tree know it's being attacked?

1:02:04 > 1:02:07Well, that's really interesting. This is a winter moth,

1:02:07 > 1:02:11and it's about to tuck in and you can see that when they eat

1:02:11 > 1:02:16the leaf, they chew the edge, and they are really messy eaters.

1:02:16 > 1:02:18Saliva's going all over the leaf.

1:02:18 > 1:02:22There's lots of dew on the leaf surface and, within that saliva,

1:02:22 > 1:02:26there are chemicals that the oak tree can recognise.

1:02:27 > 1:02:30While we might see or hear approaching danger,

1:02:30 > 1:02:31the oak senses it chemically.

1:02:33 > 1:02:37It's hard to appreciate, as we have no analogous sense,

1:02:37 > 1:02:40but it's an incredibly fine-tuned and refined system.

1:02:42 > 1:02:45This chemical signalling is really sophisticated,

1:02:45 > 1:02:49so our oak tree can tell whether it's a caterpillar

1:02:49 > 1:02:53or whether it's a different kind of herbivore like a sap sucker,

1:02:53 > 1:02:57or aphid that feeds in a different way, and it's even better than that.

1:02:57 > 1:02:59The oak tree can tell the difference

1:02:59 > 1:03:02between big caterpillars and small caterpillars.

1:03:02 > 1:03:04The age of the caterpillar can be detected.

1:03:04 > 1:03:06That is amazing.

1:03:06 > 1:03:10Once our tree has sensed it's being attacked in one place,

1:03:10 > 1:03:12it's actually able to signal to itself

1:03:12 > 1:03:14to warn other parts of the attack.

1:03:15 > 1:03:18It produces something called wound hormones,

1:03:18 > 1:03:22and those hormones move all around the plant in the sap system and

1:03:22 > 1:03:27that tells the plant to turn on its defences in other parts of the tree.

1:03:27 > 1:03:31And they also cause airborne signals to be released that also

1:03:31 > 1:03:32travel around the tree.

1:03:32 > 1:03:35So the defences are ready all over the place.

1:03:35 > 1:03:37So if one branch, if that little branch there

1:03:37 > 1:03:40was suddenly attacked by lots of caterpillars,

1:03:40 > 1:03:44the tree would know and it would protect all the rest of itself?

1:03:44 > 1:03:47It would start to, yes. It talks to itself,

1:03:47 > 1:03:51and there's a sort of chattering goes on across the whole canopy.

1:03:51 > 1:03:54Once our tree knows it's being attacked, it begins

1:03:54 > 1:03:59to produce poisons that will stop its attackers in their tracks.

1:04:00 > 1:04:02The main defences of an oak

1:04:02 > 1:04:05are chemicals called phenolics and tannins.

1:04:05 > 1:04:10That's what you have in your teacup. That's what gives tea its taste.

1:04:10 > 1:04:12Yes, tea contains a lot of tannin,

1:04:12 > 1:04:16and it's tannin that produces that bitter flavour in tea because

1:04:16 > 1:04:20the tannin binds with protein in your mouth,

1:04:20 > 1:04:23the saliva, and gives it that sort of bitter taste.

1:04:23 > 1:04:27And that's exactly what happens when the insects try and feed.

1:04:27 > 1:04:31They find that the chemicals in the oak leaves will bind to

1:04:31 > 1:04:35the proteins in their digestive system and stop them going so well.

1:04:35 > 1:04:40So, it may look like the tree is just a big, green heap of food,

1:04:40 > 1:04:42but eating it is not that easy.

1:04:42 > 1:04:44It's a real challenge to eat plants.

1:04:44 > 1:04:47They're full of defences and they're very clever,

1:04:47 > 1:04:50and they're able to detect the things that attack them.

1:04:50 > 1:04:52They've had millions of years to evolve to do that.

1:04:52 > 1:04:54And they've got a very sophisticated armoury.

1:05:02 > 1:05:06After keeping the insect hordes of early spring at bay,

1:05:06 > 1:05:09our tree can continue its rapid growth.

1:05:09 > 1:05:12But now, a new danger is emerging.

1:05:12 > 1:05:14An outlandish group of insects that

1:05:14 > 1:05:18have hijacked our oak's growth for their own ends.

1:05:19 > 1:05:22They are, without doubt, the strangest

1:05:22 > 1:05:25and most sophisticated foe our oak will face.

1:05:32 > 1:05:34This is a gall wasp.

1:05:38 > 1:05:41By laying its egg in a female oak flower,

1:05:41 > 1:05:45it causes a profound change in the way our tree grows.

1:05:48 > 1:05:52That produces a kind of tumour known as a gall

1:05:52 > 1:05:54to grow in place of an acorn.

1:05:54 > 1:05:56MUSIC: Piano Concerto No 21 by Mozart

1:05:58 > 1:06:02Inside the gall, a grub develops, feeding on the nutritious

1:06:02 > 1:06:05tissues within, while being given shelter from enemies.

1:06:08 > 1:06:11This bizarre structure is the perfect nursery.

1:06:18 > 1:06:21This particular structure is known as a knopper gall

1:06:21 > 1:06:24and it's the product of just a single species of wasp.

1:06:24 > 1:06:29These wasps always produce this type of gall.

1:06:29 > 1:06:32But there are many other species of gall wasp

1:06:32 > 1:06:35and they can induce very different shaped growths.

1:06:39 > 1:06:43The remarkable thing about galls is their sheer diversity.

1:06:43 > 1:06:45There are several hundred species of gall wasp

1:06:45 > 1:06:50and each one makes a gall of a specific shape and size.

1:06:50 > 1:06:53The goals are not just random overgrowth of the oak,

1:06:53 > 1:06:57the gall wasps are actually using chemical signals in very subtle ways

1:06:57 > 1:07:02to hijack the developmental machinery of the oak at an early stage.

1:07:04 > 1:07:08The exact way each species of wasp manages to produce such

1:07:08 > 1:07:12individual and unique galls is still somewhat of a mystery.

1:07:14 > 1:07:17But it seems they may be actually altering the oak's DNA...

1:07:18 > 1:07:22genetically engineering it to grow a home for their young.

1:07:24 > 1:07:28The myriad of different types of structures these wasps create

1:07:28 > 1:07:30for their offspring is simply staggering.

1:07:32 > 1:07:35But, of all the weird and wonderful types of oak gall,

1:07:35 > 1:07:39there's one that has a strange connection with the human race.

1:07:39 > 1:07:42One type of oak gall has shaped our history.

1:07:44 > 1:07:46That's because, for 1000 years,

1:07:46 > 1:07:49it was the source of a special kind of ink

1:07:49 > 1:07:53with which nearly all of our historical documents were written.

1:07:57 > 1:08:01Crushed, mixed with water, iron sulphate and gum arabic,

1:08:01 > 1:08:06the humble home of the andricus kollari wasp is transformed

1:08:06 > 1:08:09into a cheap and extremely long-lasting ink.

1:08:11 > 1:08:13This is the national archives at Kew.

1:08:15 > 1:08:18In the vaults of this building are housed over 1,000 years

1:08:18 > 1:08:23of British history, in the form of millions upon millions of documents.

1:08:24 > 1:08:27Stored in these unassuming boxes is our past

1:08:27 > 1:08:32and a huge amount of it is recorded in gall ink.

1:08:33 > 1:08:38So, almost any document of any importance had to be written,

1:08:38 > 1:08:42or was written using ink made from oak gall.

1:08:42 > 1:08:43That's right.

1:08:43 > 1:08:46It's the most important ink we have in Western history.

1:08:46 > 1:08:50What made it so good? As an ink.

1:08:50 > 1:08:52It's an indelible ink.

1:08:52 > 1:08:55So it's very hard to remove.

1:08:55 > 1:08:58And you can see in some of these documents here,

1:08:58 > 1:09:02these are from the trial of Guy Fawkes.

1:09:02 > 1:09:04Wow! The actual records?

1:09:04 > 1:09:09Yep, these are the actual records of Guy Fawkes' trial.

1:09:09 > 1:09:15And here, you can see a nice example of how indelible the ink is.

1:09:15 > 1:09:18So here, the scribe has made a mistake

1:09:18 > 1:09:21and, to correct his error,

1:09:21 > 1:09:25he's actually had to scrape the surface of the parchment off,

1:09:25 > 1:09:29remove the ink from the surface and then rewrite over it.

1:09:29 > 1:09:33And you can see this dark patch here and the difference in the colour,

1:09:33 > 1:09:35because this part of the ink was put on much later.

1:09:35 > 1:09:37This is a really good illustration.

1:09:37 > 1:09:42These kinds of legal documents had to be kept in ink that was

1:09:42 > 1:09:46going to last, had to be written in ink that was going to be lasting.

1:09:46 > 1:09:49So they're written on material parchment that is more durable

1:09:49 > 1:09:52and they're written with an ink that is not going to

1:09:52 > 1:09:53just vanish before your eyes.

1:09:55 > 1:09:59But oak gall ink wasn't just used for official documents.

1:09:59 > 1:10:05Everyone from poets, musicians and mathematicians to fine artists

1:10:05 > 1:10:10used this ink to record their thoughts, feelings and ideas.

1:10:10 > 1:10:13The whole of western civilisation between from about the end

1:10:13 > 1:10:17of the Roman period to the 19th century,

1:10:17 > 1:10:20our most important texts are in iron gall ink.

1:10:20 > 1:10:26It seems just a bizarre twist of fate that all of this,

1:10:26 > 1:10:30and there are how many thousands of documents here which are written

1:10:30 > 1:10:34in this ink, began because a tiny wasp

1:10:34 > 1:10:37laid an egg in oak buds that grew into a gall,

1:10:37 > 1:10:42and that provided the basis for, essentially, our recorded history.

1:10:42 > 1:10:44That's right.

1:10:44 > 1:10:48What is surrounding us is just a small fragment

1:10:48 > 1:10:51of all the documents that survive from those 1,400 years of history.

1:10:54 > 1:10:58From wasp to gall to human hands.

1:10:59 > 1:11:03This little quirk of evolution has shaped human history.

1:11:10 > 1:11:14This incredible ink brought us the Magna Carta

1:11:14 > 1:11:17and the American Declaration of Independence.

1:11:19 > 1:11:21It has brought us the music of Mozart and Bach...

1:11:23 > 1:11:27..and the drawings of Rembrandt and Leonardo da Vinci.

1:11:30 > 1:11:34Thanks to gall ink, we have Isaac Newton's theories

1:11:34 > 1:11:36and the letters of Charles Darwin.

1:11:39 > 1:11:43Unwittingly, the oak tree has enabled us to record our past,

1:11:43 > 1:11:48to express our most profound ideas and to share our deepest emotions.

1:12:00 > 1:12:03In just three months, our tree has gone through

1:12:03 > 1:12:05a radical transformation.

1:12:05 > 1:12:08It has brought out its leaves, it has spread its pollen

1:12:08 > 1:12:12for miles around, and it has repaired the damage sustained over winter.

1:12:14 > 1:12:17Now, as the insect populations grow ever larger,

1:12:17 > 1:12:22this mighty organism is finally ready to face its most challenging season.

1:12:39 > 1:12:42It's now June and, under the intense sunlight,

1:12:42 > 1:12:45trees and plants are working at full capacity.

1:12:51 > 1:12:55For the countless life forms of the forest, it's a time of plenty.

1:12:57 > 1:13:00And, at the centre of this frenetic activity is our oak.

1:13:03 > 1:13:06Right now, it's literally being eaten alive.

1:13:08 > 1:13:12There are hundreds of insects that depend on the oak for sustenance.

1:13:12 > 1:13:15But I want to see the insects us humans do not normally come across -

1:13:18 > 1:13:21the ones that live high up in the oak's canopy.

1:13:26 > 1:13:31Well, it's now the height of summer and the tree is in full leaf.

1:13:31 > 1:13:35There's even some acorns beginning to swell.

1:13:35 > 1:13:42This is just an enormous, cathedral-like space.

1:13:42 > 1:13:47What's very frustrating when you're on the ground is that you know there

1:13:47 > 1:13:53are lots of fantastic insects and animals, but you can't reach them.

1:13:55 > 1:13:59So, the only way to get to them is to climb.

1:14:01 > 1:14:04HE GRUNTS AND GASPS WITH EFFORT

1:14:07 > 1:14:10If I can just find a nice place to stand...

1:14:14 > 1:14:16Oh! There we are.

1:14:22 > 1:14:23Wow!

1:14:28 > 1:14:32This is a very privileged view of an oak tree

1:14:34 > 1:14:36and one that only an insect would have.

1:14:37 > 1:14:41There are some insects up here that you never see from the ground.

1:14:51 > 1:14:55If I can just shake the foliage, try and get some insects in the bag.

1:14:59 > 1:15:01I'll bet there's lots of good stuff in here.

1:15:01 > 1:15:05Now, the next bit of kit is the pooter.

1:15:05 > 1:15:07That allows me to suck insects out of the net.

1:15:13 > 1:15:17Without handling them, because lots of these things are very small.

1:15:20 > 1:15:22So, let's see what we've got.

1:15:22 > 1:15:25High up in our tree, there is a wealth of life.

1:15:25 > 1:15:27This is where the good stuff will be.

1:15:27 > 1:15:28Hmm!

1:15:31 > 1:15:33Oh!

1:15:33 > 1:15:36But, to get a sense of its diversity, and the unique

1:15:36 > 1:15:40adaptations of creatures up here, we have to take a closer look.

1:15:42 > 1:15:44And we can do that under the microscope.

1:15:45 > 1:15:48Now, we've got quite a few insects in here.

1:15:48 > 1:15:51- I think we'll just empty them in there, and hope for the best.- Great.

1:15:51 > 1:15:54- I'll just whack them in. - I'm sure it will be fine.

1:15:55 > 1:15:57A big earwig there, look at that!

1:15:58 > 1:16:02What is absolutely amazing with this machine is the quality of that

1:16:02 > 1:16:04image is just breathtaking.

1:16:06 > 1:16:10Well, that is the head end of a cricket,

1:16:10 > 1:16:12and she's having a preen here.

1:16:12 > 1:16:15The very interesting thing about these insects is that they

1:16:15 > 1:16:17have their ears on the knees of the front leg.

1:16:19 > 1:16:23You will see a little opening there, and that is the opening of her

1:16:23 > 1:16:26hearing organs, which are here and here.

1:16:26 > 1:16:29And, by having their ears on their front legs, quite far apart,

1:16:29 > 1:16:35they're able to triangulate and know exactly where that sound is from.

1:16:35 > 1:16:37Now, let's see if we can see anything else here.

1:16:37 > 1:16:40There are absolutely minute things in here.

1:16:40 > 1:16:44A tiny little thing, a mite, absolutely minute.

1:16:44 > 1:16:49And there are probably millions, tens of millions of these up a tree.

1:16:49 > 1:16:55That animal is tinier than the claw on the hind foot of a cricket.

1:16:56 > 1:16:59This spectacular variety of insects

1:16:59 > 1:17:01are all at their most active in summer,

1:17:01 > 1:17:06and many of them are specially adapted to eat our oak's leaves.

1:17:06 > 1:17:07This is a plant hopper

1:17:07 > 1:17:13and it's able to suck out sugary sap from individual plant cells.

1:17:13 > 1:17:15When these sap suckers attack en masse,

1:17:15 > 1:17:18it can be devastating to the delicate leaves of our tree.

1:17:20 > 1:17:24There are many, many different insect species who call our tree home,

1:17:24 > 1:17:27but there are a select few who have a special relationship.

1:17:29 > 1:17:32Species that have evolved to specifically

1:17:32 > 1:17:33take advantage of the oak.

1:17:35 > 1:17:39This is one of our tree's infant acorns, finally beginning to emerge.

1:17:41 > 1:17:44It's a beautiful, intricate structure.

1:17:47 > 1:17:50Something here is not right.

1:17:50 > 1:17:53This strange, black hole is a sign that this acorn

1:17:53 > 1:17:55has been tampered with.

1:17:55 > 1:17:59BELLS CLANG OMINOUSLY

1:17:59 > 1:18:03The culprit is one of the most highly specialised

1:18:03 > 1:18:05and bizarre species on the oak.

1:18:06 > 1:18:10DISTORTED, CLANGER-LIKE NOISES

1:18:13 > 1:18:14The acorn weevil.

1:18:21 > 1:18:24Look at that! Ho-ho!

1:18:24 > 1:18:27Is that not just the most beautiful thing?

1:18:27 > 1:18:32This is an animal that's evolved specifically with oak trees.

1:18:32 > 1:18:34It lays its eggs in acorns,

1:18:34 > 1:18:38and it's got this enormously long beak that comes out of its head

1:18:38 > 1:18:42and, at the end of that are a pair of tiny jaws,

1:18:42 > 1:18:48and it drills deep into acorns to lay its eggs in the acorn,

1:18:48 > 1:18:53and she has these peculiar antennae which are elbowed, hinged,

1:18:53 > 1:18:55and, as she drills into the acorn,

1:18:55 > 1:18:58she can fold them back along the side of the head.

1:19:00 > 1:19:06Our weevil also has highly specialised bilobed feet

1:19:06 > 1:19:09with which it's able to grip onto the smooth surface

1:19:09 > 1:19:10of the oak's acorns.

1:19:15 > 1:19:20Being able to see them this close brings you into their world.

1:19:20 > 1:19:24You can understand the mechanics of what they have to do,

1:19:24 > 1:19:25how they have to live.

1:19:35 > 1:19:38It doesn't get any better than this, really.

1:19:38 > 1:19:41That is just evolution at its most wonderful.

1:19:45 > 1:19:48The acorn weevil is just one of many insects up our tree.

1:19:49 > 1:19:53On one single branch, there's a beautiful and deadly lacewing.

1:19:53 > 1:19:59Other insect predators, such as a damsel bug and a comb-footed spider.

1:19:59 > 1:20:03And the tussock moth caterpillar, who can feast on our oak's leaves.

1:20:04 > 1:20:07All of these insects have found ingenious ways to use the oak

1:20:07 > 1:20:11for their own ends and extract food from it in some way or other.

1:20:14 > 1:20:17And it's not just insects -

1:20:17 > 1:20:19us humans also consume oak.

1:20:19 > 1:20:21In fact, we can drink it.

1:20:22 > 1:20:26To discover more about this, I'm going to the land of my forefathers.

1:20:28 > 1:20:30Scotland.

1:20:32 > 1:20:35This is the Scotch Whisky Experience in Edinburgh.

1:20:35 > 1:20:38With 3.384 different bottles,

1:20:38 > 1:20:41it's the world's largest whisky collection.

1:20:41 > 1:20:44To be legally called a Scotch whisky,

1:20:44 > 1:20:49the alcohol must be stored in oak barrels for at least three years.

1:20:49 > 1:20:52Whisky is, in essence, oak-flavoured alcohol.

1:20:53 > 1:20:58Does the growth of the oak tree effect what the whisky will

1:20:58 > 1:20:59eventually be?

1:20:59 > 1:21:01Yes, it absolutely can do.

1:21:01 > 1:21:04Generally, what happens in quercus species is,

1:21:04 > 1:21:09the tree lays down material in two distinct parts of the year,

1:21:09 > 1:21:14springtime, it lays down early wood, which is like a sponge, very porous.

1:21:14 > 1:21:18The rest of the year, late wood which is... hard and dense.

1:21:18 > 1:21:21The early wood is more porous or spongy,

1:21:21 > 1:21:24therefore it can give forth more flavour.

1:21:24 > 1:21:28So, if you're really fussy about the type of barrel you want to use,

1:21:28 > 1:21:32you will go for so-called tight-grained oak, typically,

1:21:32 > 1:21:3412-16 growth rings per inch,

1:21:34 > 1:21:37if you're going to get very specific about it!

1:21:37 > 1:21:41By treating oak barrels in different ways, by charring them

1:21:41 > 1:21:44and seasoning them with other wine and spirits, it's possible

1:21:44 > 1:21:48to release multiple chemical compounds from the oak,

1:21:48 > 1:21:51leading to an incredible diversity of whisky flavours.

1:21:51 > 1:21:58So what we've got is actually a very complicated system.

1:21:58 > 1:22:01All these compounds which give flavour to the whisky,

1:22:01 > 1:22:06how many different flavourings are there, do you think?

1:22:06 > 1:22:10I would say that there is probably between 50-100 different compounds

1:22:10 > 1:22:13we can identify that have come out of the oak wood

1:22:13 > 1:22:17that can influence the character and flavour of the whisky.

1:22:17 > 1:22:20So, when you drink your mature whisky, all these lovely,

1:22:20 > 1:22:24buttery flavours, the soft texture on the palate, the sweetness,

1:22:24 > 1:22:28the vanilla, the coconut, the almond, all of these flavours

1:22:28 > 1:22:32are drawn directly from the good-quality oak wood.

1:22:33 > 1:22:37The multitude of flavours that whiskies possess

1:22:37 > 1:22:40are testament to the complexity of the oak's wood.

1:22:48 > 1:22:51From weevil to human, there are many hundreds of species that eat

1:22:51 > 1:22:54or consume the oak in some way,

1:22:54 > 1:22:57but what does our tree eat?

1:22:57 > 1:22:59Where does it get its energy from?

1:23:01 > 1:23:03The answer is, of course, the sun,

1:23:03 > 1:23:06and at the height of summer, this process,

1:23:06 > 1:23:09famously as photosynthesis, is at its peak.

1:23:15 > 1:23:16To see how the tree does this,

1:23:16 > 1:23:19we need to look at its leaves under the microscope.

1:23:24 > 1:23:27These strange openings are called stomata.

1:23:27 > 1:23:31And they suck carbon dioxide from the atmosphere into the leaves.

1:23:35 > 1:23:39Then, powered by sunlight, this carbon dioxide is combined

1:23:39 > 1:23:44with water and turned into sugars that our tree feeds on.

1:23:45 > 1:23:47But, as they photosynthesise,

1:23:47 > 1:23:51our oak leaves perform one final, magic trick.

1:23:53 > 1:23:56Out of the many billions of stomata pours oxygen.

1:23:59 > 1:24:01It is, perhaps, the single most important

1:24:01 > 1:24:03process in the natural world.

1:24:09 > 1:24:13At the height of summer, our oak, its magnificent structure

1:24:13 > 1:24:16and its hundreds of thousands of leaves, are able

1:24:16 > 1:24:19to bask in the sunlight and convert it into food.

1:24:20 > 1:24:22In the process,

1:24:22 > 1:24:26it pumps out the oxygen that we all rely on to stay alive.

1:24:28 > 1:24:29In this single act,

1:24:29 > 1:24:32our oak is performing a feat that we have yet to match.

1:24:41 > 1:24:44As August begins, it's now been a year

1:24:44 > 1:24:47since we made the first digital model of our tree.

1:24:47 > 1:24:51Thanks to the detailed measurements we've taken over the years,

1:24:51 > 1:24:55and the weather data from Wytham Woods, it's now possible to make

1:24:55 > 1:24:58estimates that reveal the ways our tree has changed.

1:25:01 > 1:25:03Despite its age, our tree has grown.

1:25:05 > 1:25:06Over the last 12 months,

1:25:06 > 1:25:09it has been extracting carbon dioxide from the atmosphere

1:25:09 > 1:25:13through its leaves, and some of this has been refined into carbon

1:25:13 > 1:25:15and forged into new wood.

1:25:18 > 1:25:22While our oak's great size and age means that new growth

1:25:22 > 1:25:25is extremely thinly spread, it has increased in size.

1:25:25 > 1:25:31In fact, our tree has created 230 kg of new wood.

1:25:31 > 1:25:35This much material has literally been plucked from thin air.

1:25:37 > 1:25:39To help it grow and photosynthesise,

1:25:39 > 1:25:44our tree has had to consume huge quantities of water.

1:25:44 > 1:25:48Thanks to our sap flow data, we can see that, over the 71 days

1:25:48 > 1:25:56we recorded it, the tree drank an incredible 58,822 litres of water.

1:25:56 > 1:26:00But our oak tree hasn't just taken from the environment around it.

1:26:00 > 1:26:04As it photosynthesises, its leaves produce oxygen.

1:26:04 > 1:26:06Since we've been filming, our tree has released

1:26:06 > 1:26:12an incredible 234,000 litres of oxygen into the atmosphere.

1:26:12 > 1:26:16And that much oxygen is enough to keep me alive for a whole year.

1:26:22 > 1:26:26By spending a year looking at this one tree, we have been

1:26:26 > 1:26:31able to see just how dynamic and complex this organism really is.

1:26:31 > 1:26:37We have seen how it can create 700,000 leaves and keep them safe.

1:26:37 > 1:26:42We've seen how it can withstand the harsh winter conditions.

1:26:42 > 1:26:45And we've seen how our tree sits at the centre of a vast,

1:26:45 > 1:26:47interconnected web of life.

1:26:49 > 1:26:53In the face of everything thrown at it, the wind, the rain,

1:26:53 > 1:26:57freezing temperatures and constant attacks by insects and fungi,

1:26:57 > 1:26:59our tree has thrived.

1:26:59 > 1:27:01In the process, it provided a home

1:27:01 > 1:27:06and a source of food for millions of individual organisms.

1:27:06 > 1:27:08It's what makes this incredible species

1:27:08 > 1:27:11such an important part of the British countryside.

1:27:17 > 1:27:20The oak's endurance and longevity have woven it

1:27:20 > 1:27:24into the lives of the thousands of creatures that rely on it.

1:27:33 > 1:27:35And that includes us.

1:27:38 > 1:27:43This colossus of the British Isles has permeated our culture.

1:27:45 > 1:27:49Oaks have shielded us, protected us from danger.

1:27:50 > 1:27:54They have allowed us to explore the seas.

1:27:54 > 1:27:56They have brought us pleasure.

1:27:59 > 1:28:03They have helped us express our most profound ideas.

1:28:05 > 1:28:09Oaks have borne witness to our deepest sorrows

1:28:09 > 1:28:11and our most joyful moments.

1:28:16 > 1:28:21This plant, perhaps more than any other, has become part of us.